In recent years, with the developments in computer-related technology, three-dimensional image information has been easily handled. As a means for outputting three-dimensional image information handled by computers, it has been common to carry out pseudo three-dimensional display on a display. In the case of this pseudo three-dimensional display, freely moving an image displayed on a display allows the displayed image to be observed in a three-dimensional way. However, it is difficult to express three-dimensional image information sufficiently in the pseudo three-dimensional display, because no true three-dimensional image is displayed.
Therefore, devices have been researched for generating a hologram for reproducing a three-dimensional image. Patent Document 1 discloses a device for generating a transmission type hologram on a recording medium by radiating object light and reference light from the same side of the recording medium. FIG. 13 shows a section of an optical system in Patent Document 1. In Patent Document 1, light of S-polarized light emitted from a light source is converted by a spatial light modulator to predetermined light of S-polarized light or P-polarized light for each pixel, and the light is made incident to a beam splitter 37 of FIG. 13 from the side, and reflected by a semi-reflecting surface 37a. Then, light of P-polarized light of the light incident to a S-polarized light hologram 35 directly passes, as a parallel beam of light, through the S-polarized light hologram 35 to serve as reference light for recording, whereas light of S-polarized light of the light incident to a S-polarized light hologram 35 is made slightly convergent by the S-polarized light hologram 35 to serve as information light for recording. The reference light for recording and the information light for recording are made incident to a two-fraction optical rotation plate 34, and the reference light for recording, which has passed through the optical rotation plate 34L, is converted to B polarized light, whereas the reference light for recording, which has passed through the optical rotation plate 34R, is converted to A polarized light. Conversely, the information light for recording, which has passed through the optical rotation plate 34L, is converted to A polarized light, whereas the information light for recording, which has passed through the optical rotation plate 34R, is converted to B polarized light. After that, the reference light for recording is collected by an objective lens 32 to irradiate a recording medium 1, and converges to have the smallest diameter at the lower end of a guide section 5 on the rear side of the recording medium 1. In addition, the information light for recording is collected by the objective lens 32 to irradiate a recording medium 1, converges to have the smallest diameter once before the recording medium 1, and then passes through the recording medium 1 while diverging.
The reference light for recording, which has passed through the optical rotation plate 34R, and the information light for recording, which has passed through the optical rotation plate 34L are both A polarized light, and thus interfere with each other, and the interference pattern is recorded on the recording medium 1. In addition, the reference light for recording, which has passed through the optical rotation plate 34L, and the information light for recording, which has passed through the optical rotation plate 34R are both B polarized light, and thus interfere with each other, and the interference pattern is recorded on the recording medium 1. In this way, the partial hologram is formed on the recording medium 1. It is to be noted that the reference light for recording is modulated into return light by an emboss pit 5a provided at the lower end of the guide section 5, in such a way that the return light is made incident to the objective lens 32. This return light passes through the two-fraction optical rotation plate 34 and the S-polarized light hologram 35 to be made incident to the beam splitter 37, in which the amount of light partially transmits through the semi-reflecting surface 37a, and passes through a convex lens 38 and a cylindrical lens 39 to be made incident to a four-section photodetector 40. Then, this return light is used to carry out the reproduction of focus servo, tracking servo, and basic clock.
In addition, Patent Document 2 discloses a device for generating a reflection type hologram on a recording medium by placing a reflection type hologram, a concave mirror, etc. for reproducing a planar wave through the incidence of a spherical wave to the rear surface of the recording medium. In the device of Patent Document 2, spatially modulated object light is radiated as spherical waves from the surface of the recording medium, the object light composed of spherical waves transmitting through the recording medium is used to reproduce planar waves from the reflection type hologram, the concave mirror, etc., which are placed on the rear surface, and the reproduced planar waves are made incident as reference light to the recording medium from the rear surface thereof to form a reflection type hologram along with the object light radiated to the recording medium.